Friday, August 3, 2012

With discussions about on-street parking tending to focus on high-demand metered spaces in retail districts, the fact can get lost that the overwhelming majority of on-street parking in a given city serves exclusively residential areas. We tend to take these spaces for granted: in a low-density area, they typically have very low occupancy rates, making them almost invisible.

These spaces are the subject of a new study, Amenity or Necessity? Street Standards as Parking Policy, which examines the "hidden parking policy" implicit in the standards for street width established by many cities. The study calculates that these standards have produced somewhere between 740 million and 1.5 billion parking spaces along American residential streets – enough to host all of the passenger vehicles in the world – the vast majority of which are unmarked, unmetered and indeed unused. The authors estimate that the cost of construction of these spaces is in the trillions of dollars, with an annual maintenance cost in the tens of billions. These costs, the authors note, amount to approximately $1,000 annually per home.

Murfreesboro, TN street, 36 ft. wide, built circa 2005.

This parking provision is the result of minimum width requirements which, by their dimensions, automatically prescribe parking lanes (a 36-foot minimum, for instance, effectively provides two parking lanes). Noting that a requirement for wide streets is equivalent to a requirement for on-street parking in most cases, the authors interviewed a series of city transportation planners to ask a) the basis for mandating street parking and b) the basis for minimum street widths.

Interestingly, although the resulting streets often look the same under both objectives, planners claimed that the purpose of providing on-street parking is to serve as an amenity for residents and visitors, whereas minimum street widths are justified for safety reasons. As the authors note:

"[Most] respondents believed that the purpose of mandating parking was to provide extra parking, which was accomplished through the minimum street width requirement under the guise of traffic safety (rather than parking demand). In other words, street parking is an amenity, but it is provided in the name of necessity. Such 'flip flop' reasoning reflects local decision makers’ ambiguous understanding of the basis for mandating parking in street standards."

Stranger still, the authors found that width requirements for private streets are generally narrower than those for public streets, which calls into question the safety justifications behind mandated public street widths as well as undermining the amenity argument. In Las Vegas, for instance, public streets are required to be 37 feet wide, while private streets need only be 28 feet. Of the many traffic planners surveyed, none were apparently able to convincingly explain the discrepancy between the public and private standards in their cities. In light of the substantial costs associated with street construction and maintenance, however, these differential street mandates effectively serve as a subsidy for private neighborhoods.

Looking at the issue as a whole, the authors further explain:

"The key problem for the parking mandate implicit in street standards is its hidden nature. ... Street parking policy has typically been buried in street width requirements, which are supposedly based on safety concerns rather than parking demand. Many street standards do not even mention parking in descriptions of the minimum width requirement, creating the impression that these requirements solely address street needs and technical issues.

"This "camouflage" makes parking policy invisible to the public and precludes public oversight. In sharp contrast to minimum off-street parking requirements, the street parking mandate has rarely been publicly discussed or debated in the United States. Even New Urbanism supporters do not oppose street parking but allow it on narrow residential streets ... The hidden nature of this parking policy grants it legitimacy because providing streets has been widely acknowledged as a key government function. The issue could become more controversial if this function of providing streets was modified to include "providing parking..."

The study closes with two recommendations:

Unmask the hidden parking policy and subject it to public debate.

Eliminate the double standard between public and private streets, and make parking optional for residential streets.

Although the authors don't delve further into the issue in this study, I think there may be a simpler explanation for the emergence of on-street parking. A study by Michael Southworth and Eran Ben-Joseph suggests that the trend toward requiring wider and wider streets in the first half of the 20th century was in part driven by a conflict between the of the intent of the transportation engineering profession to allow unobstructed, free flowing two-way traffic on all streets and the reality that, once streets were made sufficiently wide for this purpose, drivers would, out of convenience if not necessity, simply park along the curbs, narrowing the street back down again.

With planners' recommendations that travel lanes be 11 feet in residential areas, and the minimum of seven feet occupied by a parked car, this implied roadbed widths of at least 36 feet - precisely what planning commissions and highway engineers had begun advocating for by the 1950s. In this view, on-street parking was merely a incidental effect of designing for unobstructed movement, which would help explain the confusion current planners have in accounting for the existence of both on-street parking and street width minimums, as well as the identification of speeding as the greatest problem facing residential streets.

This feedback loop of increasing required minimums proceeded in spite of the growing adoption of off-street parking minimums in the 1950s, although these produced little change in form for very low-density suburban areas. In combination with the higher density suburbs of the more recent past, however, these regulations created something that was the worst of both worlds: very wide streets so riddled with curb cuts that on-street parking was hardly available anyways (see above image).

This approach was not shared by other countries: Japan, as Paul Barter describes, adopted proof-of-parking requirements for car buyers and helped enforce the policy by continuing to build residential streets so narrow that on-street parking was essentially impossible. It may not necessarily be the best or most appropriate policy for other cities or countries, but it at least shows a logically consistent approach to the issue.

The question of how street standards and parking supply interact, though, is a key and underexplored issue, and this study may help open a needed discussion on topic.